pThis book is open access under a CC BY-NC 2.5 license.pp ppOn April 22, 1915, the German military released 167 tons of chlorine gas at Ypres, Belgium. Carried by a long-awaited wind, the chlorine cloud passed within a few minutes through the British and French trenches, leaving behind at least 1,000 dead and 4,000 injured. This chemical attack, which amounted to the first use of a weapon of mass destruction, marks a turning point in world history. The preparation as well as the execution of the gas attack was orchestrated by Fritz Haber, the director of the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry in Berlin-Dahlem. During World War I, Haber transformed his research institute into a center for the development of chemical weapons and of the means of protection against them.br br Bretislav Friedrich and Martin Wolf Fritz Haber Institute of the Max Planck Society, the successor institution of Haber's institute together with Dieter Hoffmann, Jurgen Renn, and Flo